Relation between x-ray emission mechanism and crystal structure in LiNbO₃

Abstract

x-ray emission in LiNbO 3 is confirmed by thermal treatments in a vacuum system by a new cleaning method of the crystal. Detailed single-crystal high-temperature x-ray structure refinements were carried out at 297, 323, 373, 423 and 473 K, far below the phase transition (∼1473 K). The unit cell dimensions a and V show a linear increase with temperature; however, the lattice parameter, c shows only a slight linear increase. The length of Nb-O bonds in adjacent octahedra is almost constant below 423 K. It is suggested that the valence electron in Nb changes in the compound. Therefore, x-ray emission induced by charged particles including electrons can be considered to have a close relation to the electric charge of Nb in LiNbO 3 .

Introducing a New d0 Sc3+ Asymmetric Ion for Functional Materials: Large Birefringence Enhancement by ScO6 in Ba3Sc2(BO3)4

“…[33] Ba atoms occupy the interlayer space of [Sc(BO 3 ) 2 ] ∞ layers in two coordination environments: Ba [34][35] Such C3 distortion of octahedra is commonly observed in the crystal structures of LiNbO 3 and low temperature form of KNbO 3 , NaNbO 3 and BaTiO 3 . [36][37][38][39] All values for bond distances and bond angles are consistent with previously reported values (Table S2) and the calculated bond valence sums for Sc, B and O atoms also match well with their oxidation states (Table S4). The BVS values of the two different Ba 2 + ions show strong deviations from their ideal values, which has been reported previously in the similar compound of Ba 3 Y(BO 3 ) 3 .…”

“…This observation is consistent to similar other C3 distorted d 0 state cations, e. g. Nb 5 + in rhombohedral LiNbO 3 and Ti 4 + in BaTi(BO 3 ) 2 give much enhanced birefringence from their cubic O h symmetry. [32,36] Although the birefringence of Ba 3 Sc 2 (BO 3 ) 4 is still slightly smaller than that of commercial CaCO 3 crystal from mineral sources (experimental 0.171 @ 633 nm) [58] , the difficulty of practical crystal growth and the narrow transparency range (350-2300 nm) prevent the applications of calcite crystal in special aspects of UV and laser industries. The d 0 transition metals usually bring in a drawback of strong absorption in the ultraviolet (UV) region.…”

Development of a small X‐ray source using an ultraviolet laser and pyroelectric crystal

“…For this reason, the temperature increase of the pyroelectric crystal in this work includes the temperatures of both the crystal itself and of the synthetic quartz glass. Nonetheless, the maximal temperature observed for the pyroelectric crystal in this work was 312 K, significantly lower than previous reports of heating to 353–393 K . Thus, the use of the UV laser with the pyroelectric crystal creates minimal need for cooling at present, making our pyroelectric X‐ray source a good candidate for miniaturization.…”

Atomic Substitution to Tune ScO6 Distortion in Ba2MSc2(BO3)4 (M = Na, K, Ba) to Acquire a Large Birefringence

“…Hence, the birefringence of Ba 2 K 1.6 Na 0.4 Sc 2 (BO 3 ) 4 and α-Ba 3 Sc 2 (BO 3 ) 4 crystals was measured with the use of an Axio A1 polarizing microscope (Figure a), and the obtained results are 0.11@550 nm for Ba 2 K 1.6 Na 0.4 Sc 2 (BO 3 ) 4 and 0.14@550 nm for α-Ba 3 Sc 2 (BO 3 ) 4 that match well with the DFT data. Generally speaking, the distorted d 0 octahedra are able to enhance the birefringence of oxides containing transition metals, derived by the SOJT effect, for example, LiNbO 3 and BaTiO 3 . Hence, the combination of theoretical and experimental analysis confirms that the discrepancy of birefringence (∼0.05 between the experimental value and the empirical calculated value) in α-Ba 3 Sc 2 (BO 3 ) 4 originates from the effect of distorted ScO 6 octahedral units.…”